Mobile communications such as mobile phones, wireless LAN and electric toll collection system (ETC) utilize electromagnetic waves called “centimeter waves” having a frequency band of several gigahertz (GHz).
As electromagnetic-wave absorbing sheets for absorbing such centimeter waves, Patent Document 1 proposes a stacked sheet in which a rubber electromagnetic-wave absorbing sheet and a paper sheet material (e.g., corrugated paper) are stacked. Patent Document 2 proposes an electromagnetic-wave absorbing sheet in which thin sheets containing anisotropic graphite and a binder are stacked alternately to adjust the thickness. Thereby, the electromagnetic-wave absorbing sheet can have stable electromagnetic-wave absorbing properties, regardless of the incident direction of electromagnetic waves.
Furthermore, in order to absorb electromagnetic waves in a still higher frequency band, Patent Document 3 proposes an electromagnetic-wave absorbing sheet that can absorb electromagnetic waves in the frequency band of 20 GHz or higher, which is obtained by aligning the longitudinal direction of flat soft magnetic particles with the plane direction of the sheet.
Moreover, it is known from Patent Document 4 that an electromagnetic-wave absorber that has a packing structure of particles having epsilon iron oxide (ε-Fe2O3) crystal in the magnetic phase, exhibits electromagnetic-wave absorbing performance in a range from 25 to 100 GHz.